The present invention relates to magnetic field and current sensors, a control method and a magnetic core for these sensors.
Magnetic field sensors find numerous applications in industry. For example, they are used to carry out measurements of current in the automobile or aeronautics sector.
Field sensors often use a magnetic core to concentrate the magnetic flux on the transducer so as to amplify the signal.
In general the magnetic material from which the core is made introduces undesirable non-linearities of hysteresis types which perturb the measurement and require zero-field operation, through the conventional technique of flux feedback.
Certain magnetic cores are also used as magnetic-field transducers or modulators. These cores must then exhibit strong non-linearities, characterized by a relative permeability which varies as a function of the magnetic field. The materials conventionally used to make these cores are soft magnetic alloys. To control hysteresis problems, isotropic alloys (for example Mu-metals®) or anisotropic alloys of the oriented nanocrystalline strip type are used. Whatever the material, an excitation field which will more or less saturate the material is used. Specifically, the saturation of the magnetic material creates a significant point of inflection in the magnetic cycle B(H) of these materials. This point of inflection is the non-linearity which is used to modulate the magnetic field. More precisely, the presence of an external field to be measured will increase the saturation and thus generate harmonics which will be detected. It is also possible to say that the external field is used to modulate the excitation field.
There therefore exist magnetic field sensors having:                at least one magnetic core able to modulate the amplitude of a magnetic excitation field as a function of the amplitude of the magnetic field to be measured, this magnetic core exhibiting a magnetic cycle of the magnetic induction as a function of the magnetic field devoid of hysteresis in an operating span [Hmin; Hmax], and        an electronic circuit tied to the magnetic core and able to measure the magnetic field induced in the magnetic core, this induced magnetic field resulting from the combination of the magnetic field to be measured and the magnetic excitation field.        
When the material is saturated, the relative permeability drops abruptly and the core then loses its flux concentration capability.
The invention is aimed at remedying this drawback by proposing a magnetic field sensor using a magnetic core to modulate the excitation field as a function of the magnetic field to be measured without it being necessary to saturate the magnetic core.